[vtkusers] registration in ITK and visualization in VTK - transform questions

[Michael Schildt]

Hello Everybody!

I want to display the progress of a intermodal 3D registration with an 
centered affine transform. So every iteration I catch the intermediate 
transform parameters and want to display them with VTK. It was mentioned 
often that way but i didn't find any concrete example.

       // get transform parameter in ITK
      AffineType::InputPointType C = transform->GetCenter();
      AffineType::MatrixType M = transform->GetMatrix();
      AffineType::OutputVectorType T = transform->GetTranslation();

I visualize the two datasets via outline filter as suggested in the ITK 
documentation. But I ren into some issues because of the different 
coordinate systems ITK(mathematical convetion - origin in the lower left 
corner) and VTK (graphical convention - origin in the upper left corner) 
are using:

1. I flipped the y-axis of both images using ITKs flip filter. By that 
the origin's y coordinate changes too, but that is not intended or is it?
2. How to convert efficiently between the two coordinate systems for the 
affine transform - perhaps just inverting the y-axis?
3. Related to 2. question how to put the data from ITK (center, 
translation, matrix) into the VTK AffineTransform? I would build a VTK 
4x4 Matrix from the ITK 3x3 matrix + transform. But how to integrade the 
center of rotation and scaling?

At the Moment I set Origin and Translation only:

    // vtk set transform parameter
    // moving is a vtkActor
      moving->SetOrigin(C[0],C[1],C[2]);
      moving->SetPosition(T[0],T[1],T[2]);
      renderwin->Render();

Greetings,
    Michael Schildt